SCN- is a polar molecule because of the electronegativity difference between nitrogen (3.04), sulfur (2.58), and carbon(2.55). Both Nitrogen and Sulphur attract the electrons from the Carbon atom,resulting in a partial positive charge on carbon and negative charges onnitrogen and sulfur.
Detailed Explanation: Why SCN- is a Polar molecule?
SCN- is the chemical formula of Thiocyanate which is alsoknown as Rhodanide and its IUPAC name is Cyanosulfanide. It is the conjugatebase of Thiocyanic acid and produced by the reaction of elemental sulfur withcyanide.
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Before going deep inside its polarity behavior, let’shave some basic ideas about polar and nonpolar molecules.Polar Molecules
Those molecules having polar covalent bonds within themolecule i.e. electronegativity difference between bonded atoms so that the formation of dipole charges on the molecules are known as polar molecules. Thenet dipole moment shouldn’t be zero in the case of a polar molecule.
Polar molecules show little ionic characteristics as theycan conduct heat and electricity, can be soluble in water, and have a strong electrostatic force of attraction.
Examples of Polar molecules: Water (H2O), Nitrogen Dioxide (NO2), etc.Nonpolar Molecules
Those molecules having the same electronegativity value forbonded atoms so that there are not any formation partial positive and negativecharges within the molecule results in net dipole moment become zero are knownas nonpolar molecules. In many cases, there may exist polar bonds within themolecules but whole molecules are considered as nonpolar due to the symmetricalgeometry of molecules which causes dipole charges of molecules to get canceled.
Nonpolar molecules are pure covalent bonds as they only showcovalent nature i.e. bad conductor of heat and electricity, insoluble in polarsolvents, etc.
Examples of Nonpolar molecules: Carbon Dioxide (CO2), CarbonTetrachloride (CCl4), Methane (CH4) etc.
Thiocyanate (SCN-) Polar or Nonpolar (On the basis ofcharacteristics)
SCN- is a polar molecule and the Nitrogen atom closest tonegative side as the electronegativity of Nitrogen (3.04) is greater than Sulphur(2.58) and Carbon (2.55). In this molecule, Nitrogen pulls the electrons fromboth sulfur and carbon but E.N difference between Nitrogen and Sulphur is verysmall so they can donate electrons within a reaction from either end of themolecule.
These are some of the characteristics of SCN- which show whyit is considered as a polar molecule:Electronegativity Difference
Electronegativity is the tendency of an atom to attract a shared pair of electrons within a molecule. Higher the E.N means the atom has a higher tendency to attract the lone pairs of electrons from a bonded partner.
According to thePauli scale, the electronegativity difference oftwo atoms is between 0.4 to 1.7, it is considered as polar bonding between theatoms. In SCN,
E.N of Nitrogen= 3.04
E.N of Sulfur= 2.58
E.N of Carbon= 2.55
Here electronegativity difference between nitrogen andcarbon is 0.49 which causes the formation of a partial positive charge on the carbon atomand partial negative charge on nitrogen i.e. bond is polar as a result moleculeis also polar.
Also Read: Is HCl Polar or Nonpolar Molecule?Lewis Structure & Molecular Geometry
SCN- has a total of 16 valence electrons participated in molecule formation and there is not any lone pair of electronson the central C atom. So, no electron-electron repulsion takes place inside themolecule.
The dipole moment is a product between the charge and distancebetween the bonded atoms. It means higher the electronegativity differencebetween the atoms higher the value of the net dipole moment, only if dipole chargesdo not cancel each other. In SCN-, sulfur and nitrogen have higherelectronegativity value than carbon so that carbon atom has a partial positivecharge and the remaining atoms have partial negative charges induced.Electron Density
Electron density is the possibility of electrons within themolecule being present at a dedicated place. But due to the electronegativitydifference between the atom, atoms having higher E.N value pull electronstowards themselves. Same in this SCN molecule, Sulfur, and Nitrogen havinghigher E.N so that they attract electrons from the central Carbon atom.Solubility Principle
According to the solubility principle “Like dissolves like”, SCNis soluble in polar solvents like water, ammonia, most alcohols, hydrogenfluoride, etc, and insoluble in nonpolar solvents like benzene, acetone, carbontetrachloride, etc (some exceptions always exist).
Sources of Thiocyanate (SCN-)
1. It is found in cigarette smoke and various plant foods likecabbage, turnips, broccoli, and cauliflower.
2. In the human body, it is found in blood, feces, urine, andsaliva. It is also found inside the cell in mitochondria and cytoplasm.
3. Synthetically, it is formed by the reaction between cyanideand S-S bonds compound in the presence of an aqueous medium.
Properties of SCN-It is soluble in water and most of the polar solvents.It shows an extremely strong acidic nature.Thiocyanate is considered a little toxic molecule due toits association with cyanide and thiosulfate.
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